fix(android): Keep a newer NDK tombstone marker

Crash service workers for processes that crash close together can
finish out of order. A worker that wrote an older tombstone timestamp
let `TombstoneIntegration` report the newer crash again on the next
launch.

Write the marker only when it is newer than the current one, and
serialize the workers.

Author: jpnurmi

sentry-android-ndk-outproc/src/main/java/io/sentry/android/ndk/SentryNdkCrashService.java

@@ -28,6 +28,7 @@
 import io.sentry.android.core.cache.AndroidEnvelopeCache;
 import io.sentry.android.core.internal.tombstone.TombstoneParser;
 import io.sentry.ndk.SentryNdk.CrashDaemon;
+import io.sentry.util.FileUtils;
 import java.io.BufferedInputStream;
 import java.io.Closeable;
 import java.io.File;
@@ -625,15 +626,24 @@ ApplicationExitInfo findMatchingExitInfo(
     return mergedFile;
   }
 
-  private void writeLastTombstoneMarker(final @NotNull File envelopeFile, final long timestamp)
-      throws IOException {
+  // workers for concurrent crashes must not move the marker back
+  private static synchronized void writeLastTombstoneMarker(
+      final @NotNull File envelopeFile, final long timestamp) throws IOException {
     final @Nullable File runDir = envelopeFile.getParentFile();
     final @Nullable File nativeDir = runDir != null ? runDir.getParentFile() : null;
     final @Nullable File cacheDir = nativeDir != null ? nativeDir.getParentFile() : null;
     if (cacheDir == null) {
       return;
     }
     final File marker = new File(cacheDir, AndroidEnvelopeCache.LAST_TOMBSTONE_REPORT);
+    final @Nullable String lastTimestamp = FileUtils.readText(marker);
+    try {
+      if (lastTimestamp != null && Long.parseLong(lastTimestamp.trim()) >= timestamp) {
+        return;
+      }
+    } catch (NumberFormatException ignored) {
+      // overwrite an invalid marker
+    }
     try (final OutputStream outputStream = new FileOutputStream(marker)) {
       outputStream.write(String.valueOf(timestamp).getBytes("UTF-8"));
     }

sentry-android-ndk-outproc/src/test/java/io/sentry/android/ndk/SentryNdkCrashServiceTest.kt

@@ -194,6 +194,22 @@ class SentryNdkCrashServiceTest {
     assertThat(marker().readText()).isEqualTo("2000")
   }
 
+  @Test
+  @Config(instrumentedPackages = ["io.sentry.ndk"], shadows = [CrashDaemonShadow::class])
+  fun `keeps a newer marker`() {
+    val service = Robolectric.setupService(SentryNdkCrashService::class.java)
+    val envelope = writeNativeEnvelope(timestamp = 1000)
+    addExitInfo(service, pid = 1, timestamp = 2000, trace = tombstone())
+    crashDaemon(envelope, CrashDaemon.SendResult.SENT)
+    marker().writeText("3000")
+
+    configureDaemon(service, pid = 1, fd = 10, tombstoneEnabled = true)
+    awaitWorker()
+
+    assertThat(CrashDaemonShadow.sends).containsExactly(listOf("${envelope.path}.merged", 2000L))
+    assertThat(marker().readText()).isEqualTo("3000")
+  }
+
   @Test
   @Config(instrumentedPackages = ["io.sentry.ndk"], shadows = [CrashDaemonShadow::class])
   fun `writes no marker when the send fails`() {